This invention relates to an expandable polymeric composition of matter and method of preparation, and more particularly to an expandable alkenyl aromatic polymer composition with a volatile blowing agent and a transient foam control agent.
Alkenyl aromatic polymer foams such as polystyrene foams have found a wide variety of usages including insulation, cushion packaging, and the formation of molded articles such as cups, trays, and the like. When utilized as an extruded board insulating material, a fugitive blowing agent is normally incorporated into the heat plastified polymer and the resulting mixture extruded to a zone of lower pressure and allowed to expand. Existing blowing agents preferentially include the chlorofluorocarbons (CFC's) due to their ease of use and the resulting exceptional foam properties. However, questions regarding the long term effect of CFC's in the environment have caused manufacturers to seek ways to reduce the quantity of CFC's required to produce a given density of foam (generally lower density foams utilize larger quantities of CFC's) or to utilize other, less effective blowing agents, which are not suspected of environmental damage. In order to accomplish these desirable ends it is necessary to provide a molten polymer mixture having improved (reduced) viscosity and other properties in order that reduced amounts of CFC's or other less effective blowing agents may be employed.
In the past, attempts have been made to utilize plasticizers and/or plasticizing blowing agents in polystyrene foams to aid in melt foaming, particularly where very low densities are desired Such plasticizers have been found to have an adverse effect on the final foam properties, and in some instances have resulted in a permanent softening of the foam.
Crosslinking of the foam during foaming to stabilize cell formation has also been attempted. However, the use of crosslinking agents must be carefully controlled as insufficient crosslinking does not produce the desired stabilization and over crosslinking makes processing difficult. Moreover, crosslinking of such foams makes reprocessing of the foam scraps difficult.
Accordingly, the need still exists in the art for a means to prepare extruded alkenyl aromatic polymer foams to enable reduction or elimination of CFC blowing agents.